During the construction of imaging bundles, small diameter glass fibers are drawn, guided to a drum, and wound side by side to form a ribbon around the drum. When the ribbon count is reached, the drum is indexed rapidly in the opposite direction to provide a space between each ribbon and the process is repeated until the drum has been filled. The smaller the diameter of the fiber, the better the optical performance of the bundle can be achieved in terms of resolution of small geometry images. Other factors concerning optical performance include packing density or per cent active area, and uneven packing in geometry which causes image distortion, and broken or dead fibers.
Bundles may be formed using a process in which ribbons are removed from the drum and stacked one on top of the other in a stacking tool in which pressure from top and side is applied to increase the packing density. After the stacking process is complete, the ribbons are glued together, the bundle is cut at the center of the fused region, and the bundle ends are coherent with respect to one another. However, during the stacking procedure, if the ribbons are inadvertently rotated 180 degrees, the rotated ribbon has its fiber shifted, thereby destroying the coherence of that particular element relative to the others. The performance of the optical bundle will be significantly decreased. Although the best and closest alignment of the fibers occurring during the drawing/winding process, much of the perfection is lost during stacking. Compressing the ribbons from top and side very often breaks fibers and distorts the geometry of the ribbon.
A need has thus arisen for a process to construct a coherent imaging bundle in which ribbons are wound one on top of the other while fiber transverses in the same direction on a drum. In this manner, the coherence of the bundle will be preserved with ribbons accurately stacked.